TECHNICAL FIELD

This invention relates generally to electrically controlled fuel injectors and, more particularly, to fuel injectors with a directly controlled dual concentric check valve.

BACKGROUND

In a dual fuel engine, a fuel injector is used to inject liquid fuel, such as diesel distillate, into the engine cylinder, and a second system is responsible for delivering a second type of fuel, such as natural gas. For such dual fuel engines it is desirable to be able to inject two distinct quantities of liquid fuel. A small pilot injection of diesel fuel is used to assist in ignition of a main charge of gaseous fuel when the engine is operating in dual fuel mode. However, when gaseous fuel is unavailable, or for some other reason diesel-only operation of the engine is desired, a larger injection of only diesel is made.

In the past, it would have been necessary to use two separate fuel injectors, or at least two separate nozzle assemblies in an engine with these operating requirements. One nozzle would have been necessary for the small initial pilot injection, and a second nozzle would have been necessary for the larger diesel-only injection. Such systems tend to be complex and difficult to control. It is thus desirable to create a system capable of fulfilling the dual fuel injection requirements with a single injector.

A dual concentric check design is known in the art. Lauren W. Burnett invented one example of such an injector in 1989 that could be used to inject both liquid fuel and slurry fuel through concentric nozzle outlets. It is shown in U.S. Pat. No. 4,856,713. However, this injector is not directly controlled, and designed for a liquid or slurry mixture injection rather than for use in a dual fuel engine.

A typical diesel engine must operate with a broad range of fuel quantities and operating speeds. The necessary precision of injection timing, injection duration, and the provision of sufficient pressure are difficult to accomplish with a single fuel injector. Direct control allows for better performance by enabling the precise control of injection timing and duration. As a result, the engine operates more efficiently and the fuel burns more completely, producing lower emissions.

The present invention is directed to overcoming one or more of the problems and disadvantages set forth above.

SUMMARY OF THE INVENTION

A directly controlled dual concentric check fuel injector has an injector body that defines a nozzle chamber, a check control chamber, and a plurality of nozzle outlets. A dual concentric check assembly is at least partially positioned in the injector body, and has a closing hydraulic surface exposed to fluid pressure in the check control chamber. The dual concentric check assembly is movable between a first position in which the nozzle outlets are blocked, a second position in which a first portion of the nozzle outlets are open, and a third position in which a second portion of the nozzle outlets are open.

In another aspect, a method of injecting fuel includes a step of providing a fuel injector with a plurality of nozzle outlets and a directly controlled dual concentric check assembly. The check assembly has a closing hydraulic surface exposed to fluid pressure in a check control chamber. The check control chamber is connected to a low pressure passage. The check assembly is moved to a configuration in which at least a portion of the nozzle outlets are open. Finally, the check control chamber is connected to a high pressure passage.

In still another aspect, the dual fuel engine includes a plurality of directly controlled dual concentric check fuel injectors attached to an engine housing. Each of these injectors has a dual concentric check assembly at least partially positioned in the injector body. Each of the assemblies has a closing hydraulic surface that is exposed to fluid pressure in a check control chamber. The dual concentric check assembly is movable between a first configuration in which the nozzle outlets are blocked, a second configuration in which a first portion of the nozzle outlets are open, and a third configuration in which all of the nozzle outlets are open. A source of liquid fuel is fluidly connected to the fuel injectors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a partial diagrammatic representation of a dual fuel engine that includes a dual concentric direct operated check fuel injector according to the present invention;

FIG. 2

is a diagrammatic sectioned side view of the preferred embodiment of the fuel injector from

FIG. 1

;

FIG. 3

is a diagrammatic representation of a pump-line-nozzle fuel injection system that includes another embodiment of a dual concentric direct operated check fuel injector according to the present invention; and

FIG. 4

is a diagrammatic sectioned side view of the fuel injector of FIG.

3

.

DETAILED DESCRIPTION

The present invention combines the high efficiency of direct control with a single fuel injector capable of delivering two distinct quantities of fuel. It employs a dual concentric check assembly

72

operated with an electrically actuated direct control valve assembly.

The injector has dual-check nozzles with separate orifices for pilot and main injection that are operated by electronic actuator control. The outer check has a relatively low valve opening pressure and controls a set of orifices with a smaller flow area. The inner check has a relatively high valve opening pressure and controls a set of spray orifices with a relatively large flow area. Combined with a standard unit pump or high pressure fuel common rail, the dual concentric check design provides a fuel injection system capable of higher initial injection pressures. The result is an improvement of the combustion bum quality, especially at part engine loads. To achieve improved delivery ratios between the fuel delivery from the outer check outlets alone, and the fuel delivery with both checks open, electronic direct control is necessary.

Referring to

FIG. 1

, there is shown a system level diagram of a dual fuel engine

10

application of a dual concentric direct operated fuel injector

16

according to the present invention. Either version of the fuel injector described herein can be utilized in dual fuel engine

10

, which would employ a plurality of such injectors attached to an engine housing. The method of supplying pressurized fuel within engine

10

may be with a high pressure common rail

26

, but it might also be accomplished with a plurality of electronic unit pumps connected to each injector or any other suitable method known in the art. Engine

10

also has a source of gaseous fuel fluidly connected to the engine housing. Engine

10

is capable of operation with a combination of liquid and gaseous fuel or liquid fuel alone. Engine

10

has a fuel injector

16

according to the present invention whose tip

18

protrudes into cylinder

12

. Liquid fuel from liquid fuel supply

26

is supplied to injector

16

via liquid fuel supply line

28

. The injection of liquid fuel into cylinder

12

is controlled by an electrical actuator

20

attached to injector

16

. Electrical actuator

20

is controlled with electronic control module

22

via communication line

24

in a conventional manner. When electrical actuator

20

is energized, liquid fuel is injected into cylinder

12

via injector tip

18

.

When dual fuel operation is desired, gaseous fuel from gaseous fuel supply

30

is supplied via gaseous fuel supply line

32

to cylinder

12

, controlled by control valve

36

. The opening and closing of control valve

36

is achieved with electronic actuator

38

, itself controlled in operation by electronic control module

22

via communication line

40

in a conventional manner.

The combustion of liquid and/or gaseous fuel in cylinder

12

creates force that acts on piston

14

. In dual fuel mode, the compression ignition of the diesel fuel pilot injection ignites the gaseous fuel from the main injection. This provides the force that acts on piston

14

. In diesel-only mode, the compression ignition of the liquid diesel fuel alone creates the force that acts on piston

14

. A check valve

34

positioned within gaseous supply line

32

prevents the leaking of pressure out of cylinder

12

through gaseous supply line

32

during combustion.

Referring to

FIG. 2

, there is shown a diagrammatic sectioned side view of a direct control dual concentric check fuel injector

16

according to the present invention. The injector shown in

FIG. 2

is the preferred embodiment of the present invention and may employ either a high pressure fuel common rail system or an electronic unit pump as the means of pressurizing fuel. Fuel injector

16

consists of an injector body

50

made up of various components attached to one another in a manner well known in the art, and a number of movable parts positioned in the manner they would be at the initiation of an injection event. As discussed with regard to

FIG. 1

, liquid fuel source

26

, either a high pressure fuel common rail or an electronic unit pump, supplies pressurized fuel to injector

16

through liquid fuel supply line

28

. The pressurized fuel enters injector

16

through fuel inlet

51

, defined by injector body

50

, and is supplied thenceforth to a pressure communication passage

56

(high pressure passage) and a nozzle supply passage

52

, both defined by injector body

50

. Pressure communication passage

56

is in constant fluid communication with a control volume

69

, defined by injector body

50

. The present invention uses pressurized fuel as the control hydraulic fluid, though it should be appreciated that engine oil, transmission, power steering, brake, coolant, or some other suitable engine fluid might be used.

Fuel injector

16

is controlled in operation by a control valve assembly

60

, preferably attached to and located within the injector itself. Control valve assembly

60

has an electrical actuator

20

that is preferably a solenoid. It should be appreciated, however, that another suitable device such as a piezoelectric actuator might be used. Solenoid

64

has a coil

66

, and an armature

67

, which is attached to a control valve member

62

. An electrical connector

21

connects solenoid

64

with the control module

22

. A biasing spring

65

biases armature

67

and solenoid

64

toward their upward position closing low pressure seat

70

.

Control valve member

62

has been shown as a poppet valve, though it should be appreciated that another suitable valve type, such as a spool, might be used. Control valve member

62

is movable within injector body

50

between an upward (off) position in which it closes low pressure seat

70

and a downward (on) position in which it closes high pressure seat

71

.

When solenoid

64

is de-energized and control valve member

62

is in its upward position closing low pressure seat

70

, control volume

69

provides fluid communication between pressure communication passage

56

and needle (check) control chamber

57

. The high pressure fluid supplied to needle control chamber

57

exerts a downward force on closing hydraulic surface

85

of piston

84

. When solenoid

64

is energized, and control valve member

62

is in its downward position closing high pressure seat

71

, internal passage

63

provides fluid communication between needle control chamber

57

and vent passage

58

. Vent passage

58

is relatively low pressure and connects to a vent outlet

59

defined by injector body

50

. The up or down state of control valve member

62

thus determines whether there is hydraulic pressure acting on the hydraulic surface of piston

84

and, as discussed below, whether the dual check nozzle outlets

54

and

55

are open or closed.

Within injector body

50

, piston

84

abuts an outer check coupler

83

that in turn attaches to outer check extension

82

. Outer check extension

82

abuts an outer check needle member

81

. The outer check

80

is comprised of piston

84

, outer check coupler

83

, outer check extension

82

, and outer check needle member

81

. Outer check

80

moves up and down within injector body

50

to open and close outlets

54

. An outer check biasing spring

89

exerts a downward force on outer check coupler

83

, biasing the assembly toward a down position in which outer check needle member

81

is held to close outer check seat

73

. Seated thusly, outer check

80

closes a first set of nozzle outlets

54

distributed radially around a centerline

19

and fluidly isolates inner check

90

from nozzle chamber

53

. Thus, when electrical actuator

20

is de-energized, and closing hydraulic surface

85

of piston

84

is exposed to high pressure fuel, the entire outer check assembly

80

is biased downward against outer check seat

73

, closing the outer check nozzle outlets

54

.

Housed in part within outer check extension

82

and in part within outer check needle member

81

is an inner check

90

which is mechanically biased downward by an inner check biasing spring

95

to close inner check seat

74

. Inner check

90

thus holds closed the inner check nozzle outlets

55

that are distributed radially around the centerline

19

of injector

16

. Inner check

90

moves up and down within a center passageway

96

defined in part by outer check needle member

81

and in part by outer check extension

82

. Inner check

90

is preferably guided in its movement by a matched clearance with outer check needle member

81

.

As described above, high pressure fuel is continuously supplied to nozzle chamber

53

via nozzle supply passage

52

. Inside nozzle chamber

53

, the high pressure fuel exerts an upward force on the outer check opening hydraulic surfaces

86

. When outer check

80

opens, inner check

90

becomes fluidly connected to nozzle chamber

53

and high pressure fuel can act on the inner check opening hydraulic surfaces

91

.

The area of piston closing hydraulic surface

85

and the strength of outer check biasing spring

89

are preferably such that outer check nozzle outlet

54

is held closed in spite of the constant opening hydraulic force on its opening hydraulic surfaces

86

when pressure communication passage

56

is open to needle control chamber

57

. Those skilled in the art will appreciate that opening hydraulic surfaces

86

are preferably sized such that outer check

80

will open when needle control chamber

57

is fluidly connected to low pressure passage

58

. The outer check valve opening pressure (VOP) is defined by the pressure in low pressure passage

58

, the area of piston hydraulic surface

85

, the strength of biasing spring

89

, and the effective area of opening hydraulic surfaces

86

.

The valve opening pressure of inner check nozzle outlet

55

is defined by the strength of inner check biasing spring

95

and the size of inner check opening hydraulic surfaces

91

. In the preferred embodiment, the relevant parts of the injector are sized such that the outer check VOP is relatively low as compared to the inner check VOP. Additionally, the flow area of outer check nozzle outlets

54

is preferably significantly less than the flow area of inner check nozzle outlets

55

. However, different application of the invention might call for a different flow area relationship.

Referring to

FIG. 3

, there is shown a diagrammatic representation of a pump-line-nozzle system

110

that has a dual concentric check DOC controlled fuel injector

116

according to another embodiment of the present invention. In contrast to the high pressure fuel common rail system, the system pictured in

FIG. 3

employs an electronic unit pump

126

for pressurizing and supplying fuel to injector

116

via liquid fuel supply line

128

. Adjusting timing and duration of the electronic unit pump

126

controls peak fuel pressure in high pressure line

128

, that is, low pressure prevails in high pressure line

128

between injection events.

Referring to

FIG. 4

, there is shown a diagrammatic sectioned side view of a dual concentric check DOC controlled fuel injector

116

according to the embodiment of the present invention shown in FIG.

3

. Injector

116

operates in a similar manner to the preferred embodiment of the present invention, but with several significant differences. Like injector

16

, injector

116

is supplied with high pressure fuel via a supply line

128

. In contrast to injector

16

, the control valve assembly

160

employs a controlled leakage strategy to control pressure. After the fuel enters injector body

150

through fuel inlet

151

, the high pressure fuel travels through nozzle supply passage

152

to a nozzle chamber

153

, and through pressure communication passage

156

to a control valve assembly

160

. Control valve assembly

160

consists of an electrical actuating device

164

and a valve member

162

that moves up and down within injector body

150

. Electrical actuator

164

consists of a coil

166

and an armature

167

that is attached to control valve member

162

. Electrical actuator

164

is preferably a solenoid, but like injector

16

another suitable device might be used.

When actuator

164

is de-energized, armature

167

and thereby control valve member

162

are biased downward by biasing spring

165

. Control valve member

162

is positioned partly within the top of piston

184

. Fuel in check control chamber

157

can flow past high pressure seat

171

and around control valve member

162

to act on closing hydraulic surface

185

of piston

184

. The fuel then drains through leak passage

178

and out vent outlet

195

. It should be appreciated that the inside diameter

177

of piston

184

and the outside diameter

169

of control valve member

162

should be sized such that pressurized fuel can flow around control valve member

162

and to leak passage

178

. However, if the clearance between inside diameter

177

and outside diameter

169

is too large, fuel will leak past control valve member

162

at an unacceptably high rate. If the clearance is too small, fuel cannot flow through fast enough and the pressure drop in check control chamber

157

can be too delayed and unpredictable to allow accurate timing of injection. The hydraulic force acting on closing hydraulic surface

185

of piston

184

biases piston

184

downward. As a result, outer check

180

holds outer check nozzle outlet

154

closed in a manner similar to that employed in injector

16

. Inner check

190

operates in much the same way that inner check

90

does in injector

16

. Outer check

180

's VOP is defined by the pressure in leak passage

178

, the strength of biasing spring

189

, the area of piston closing hydraulic surface

185

, and the area of outer check

180

's opening hydraulic surface.

It should be appreciated that the relative area of piston closing hydraulic surface

185

, the strength of outer check biasing spring

189

, and the area of outer check opening hydraulic surfaces

186

are preferably such that outer check

180

will open when control valve member

162

closes high pressure seat

171

. However, outer check

180

preferably remains closed when control valve member

162

is in its down position, and high pressure seat

171

is open. Inner check

190

's VOP is defined by the area of inner check opening hydraulic surfaces

191

and the strength of inner check biasing spring

195

. It should be appreciated that the area of inner check opening hydraulic surfaces

191

and the strength of biasing spring

195

are preferably such that inner check

190

's VOP is less than the VOP of outer check

180

.

When electrical actuator

164

is energized, control valve member

162

moves toward its upward position. When control valve member

162

reaches the upper limit of its travel, it closes high pressure seat

171

and thereby blocks fluid communication between pressure communication passage

156

and control chamber

157

. As a result, the hydraulic pressure on closing hydraulic surface

185

of piston

184

drops dramatically due to the controlled leakage through vent passage

178

. Consequently, piston

184

exerts very little downward force on outer check

180

. In the preferred embodiment, pressurized fuel acting on the outer check opening hydraulic surfaces

186

can force the outer check

180

to open outer check nozzle outlets

154

and inject fuel into the combustion space when high pressure seat

171

is closed, but not when seat

171

is open. This embodiment of the present invention might in theory be used with either a common rail or unit pump hydraulic system.

However, the controlled leakage embodiment presents significant problems when used with a common rail system. Continuous leakage of fuel makes the maintenance of sufficient pressure in the common rail problematic and the wastage of energy unacceptable. Therefore, this second embodiment of the present invention should preferably employ an electronically controlled unit pump or some other periodic pressurizing device as the means of pressurizing fuel.

INDUSTRIAL APPLICABILITY

In the preferred embodiment of the present invention, prior to an injection event, solenoid

64

is de-energized and control valve member

62

is biased toward its up (off) position by the force of biasing spring

65

. In this state, control valve member

62

closes low pressure seat

70

. Control volume

69

fluidly connects needle control chamber

57

and pressure communication passage

56

. Thus, high pressure prevails in needle control chamber

57

and acts on piston closing hydraulic surface

85

. The high pressure acting on piston closing hydraulic surface

85

and the force of spring

89

bias outer check

80

downward against outer check seat

73

to close outer check nozzle outlets

54

. When outer check

80

is held against outer check seat

73

, inner check

90

is fluidly isolated from nozzle chamber

53

, and is held closed by the force of inner check biasing spring

95

. Nozzle chamber

53

is always supplied with high pressure fuel via nozzle supply passage

52

, regardless of the state of control valve assembly

60

.

When an injection event is desired, solenoid

64

is energized whereby control valve assembly

60

and control valve member

62

begin to move downward, opening low pressure seat

70

. When low pressure seat

70

is opened, internal passage

63

provides fluid communication between control volume

69

and vent passage

58

. At the instant that low pressure seat

70

is opened, both pressure communication passage

56

and needle control chamber

57

are exposed to relatively low pressure. However, when control valve member

62

reaches the downward limit of its travel, it closes high pressure seat

71

. It should be appreciated that the distance control valve member

62

must travel to close high pressure seat

71

is relatively small, and the assembly travels relatively quickly.

When high pressure seat

71

is closed, the internal passage

63

of control valve member

62

ceases to provide fluid communication between control volume

69

and vent passage

58

, but continues to fluidly connect needle control chamber

57

with vent passage

58

. As a result, the hydraulic pressure in needle control chamber

57

drops dramatically. There is no longer substantial hydraulic pressure acting on closing hydraulic surface

85

and only the force of biasing spring

89

acts to push outer check

80

downward.

Recall that nozzle chamber

53

is always exposed to high pressure fuel via nozzle supply line

52

, and thus high pressure fuel is continuously acting on the outer check opening hydraulic surfaces

86

. The force on outer check opening hydraulic surfaces

86

thus pushes outer check

80

up away from seat

73

, and high pressure fuel in nozzle chamber

53

sprays out outer check nozzle outlets

54

into the combustion space. When outer check

80

opens, the opening hydraulic surfaces of inner check

90

become exposed to the high pressure fuel in nozzle chamber

53

. Whether there is sufficient pressure to overcome the VOP of inner check

90

is controlled by adjusting the pressure of the fuel supplied by the common rail or electronic unit pump.

Recall that the valve opening pressure (VOP) of outer check

80

is defined by the strength of biasing spring

89

and the size of outer check opening hydraulic surfaces

86

. Similarly, the VOP of inner check

90

is defined by the strength of inner check biasing spring

95

and the size of inner check opening hydraulic surfaces

91

. In dual fuel mode operation, where injection of only a relatively small amount of liquid fuel is desired, the fuel pressure should be set such that it is sufficient to overcome the VOP of the outer check, but insufficient to overcome the VOP of the inner check. In this manner, the quantity of liquid fuel injected is relatively small given the relatively small flow area of the outer check nozzle outlets

54

. For a single fuel application the fuel pressure should be adjusted such that it is sufficient to overcome the VOP of both the outer check

80

and the inner check

90

. With the pressure adjusted accordingly, an injection event will occur whereby both checks are opened and fuel sprays through the relatively large combined flow areas of nozzle outlets

54

and

55

.

Shortly before the desired amount of fuel has been injected, the current to solenoid

64

is shut off. Control valve member

62

opens high pressure seat

71

and begins to move back toward its upward (off) position. When high pressure seat

71

is opened, needle control chamber

57

is once again exposed to high pressure fuel from pressure communication passage

56

via control volume

69

. With the assistance of biasing spring

89

, the high pressure in needle control chamber

57

exerts downward force on piston closing hydraulic surface

85

, and pushes the entire outer check

80

down against outer check seat

73

. This closes outer check nozzle outlets

54

, and fluidly isolates the inner check opening hydraulic surfaces

91

from nozzle chamber

53

. Consequently, inner check biasing spring

95

forces inner check

90

down against seat

73

to close inner check nozzle outlets

55

, and the injection of fuel through both sets of nozzle outlets ceases.

The second embodiment of the present invention, shown in

FIG. 4

, also allows direct control of the injection event. This version does not have a low pressure seat, but instead employs a controlled leakage to provide low pressure in control chamber

157

when injection is desired. Between injection events, the electrical actuating device is de-energized, and control valve assembly

160

is in its downward position. High pressure seat

171

is open, and high pressure fuel flows around control valve member

162

to act on piston

184

's closing hydraulic surface

185

. The hydraulic pressure assists in holding the outer check closed in a very similar manner to that employed in injector

16

. In this de-energized state, the pressurized fuel flows out leak passage

178

at a relatively constant rate.

When an injection event is desired, electrical current is supplied to actuating device

164

, and the control valve assembly begins to move upward. When control valve member

162

reaches the upper end of its travel, it closes high pressure seat

171

. As a result, high pressure fuel is blocked from flowing past control valve member

162

and acting on piston closing hydraulic surface

185

. The controlled leakage out passage

195

allows the pressure in control chamber

157

to drop. In a manner similar to injector

16

, the high pressure fuel in nozzle chamber

153

may act to open outer check

180

and/or inner check

190

, depending on whether single fuel or dual fuel operation of the engine is desired.

Shortly before the desired amount of fuel has been injected, electrical actuating device

164

is de-energized. Control valve member

162

begins to move to its downward position, and opens high pressure seat

171

. As high pressure seat

171

opens, pressurized fuel begins to flow around control valve member

162

, and hydraulic pressure once again acts on piston closing hydraulic surface

185

. The resultant closing of outer check

180

and

190

takes place in a very similar way to the preferred embodiment of the present invention.

The present invention allows precise control of fuel injection in an engine that operates on a single liquid fuel or a combination of liquid and gaseous fuel. By simply varying the pressure at which the fuel is supplied to the injector, a relatively small or a relatively large quantity of fuel can be injected. This system is advantageous because it allows the high efficiency of direct control to be combined with the versatility of a dual fuel engine. Direct control allows the injection of two discrete quantities of fuel. Furthermore, the present invention can be operated with one of two different fuel pressurization systems, adding further versatility.

It should be understood that the present description is for illustrative purposes only and is not intended to limit the scope of the present invention in any way. Although the invention was described in the context of a dual fuel engine, other engines could benefit from the present invention. For example, a dual concentric check might be employed where injection of different quantities of fuel is desired for reasons other than dual fuel operation, like different engine operating speeds or varying engine loads. Those skilled in the art will recognize that direct control of the present invention could allow for split injections. Alternately energizing and de-energizing the electrical actuator could allow for a variety of injection schemes. Small point injections might be made sequentially or might be alternated with larger main injections, depending on the operating conditions. Thus, those skilled in the art will appreciate that various modifications could be made to either of the described embodiments without departing from the intended scope of the present invention.

Other aspects and features of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.